Error control coding for future digital cellular systems

Land mobile radio channels are modeled as fading dispersive channels, because of the multipath propagation and the randomly changing medium characteristics. Many types of impairments are observed on these channels such as multipath spread (or delay spread), fading, Doppler spread, nonlinear distortion, frequency offset, phase jitter, impulse noise, thermal noise, and co-channel and adjacent channel interference arising from spectrum sharing. This chapter concentrates on the effects of delay spread, fading, Doppler spread, thermal noise, and co-channel interference. Delay spread causes interference between adjacent symbols, known as intersymbol interference (ISI), a large Doppler spread indicates rapid channel variations and necessitates a fast convergent algorithm when an adaptive receiver is employed, and fading results in a very low received signal-to-noise ratio or signal-to-interference ratio when the channel exhibits a deep fade.

This paper presents the performance analysis of quadrature amplitude modulation (QAM) using decisionfeedback equalization (DFE) over a cellular radio channel with frequency-selective fading and cochannel interference (CCI). With infinite taps the decision-feedback equalizer has been shown to be superior to linear equalizer in reducing both the intersymbol interference (ISI) and CCI. However, only equalizers with a few taps can be realized in the practical receiver design. In contrast to the noise-limited case, our simulation results reveal that the DFE can not outperform the linear equalizer (LE) using the same finite taps when CCI dominates the overall system performance. The modulation and statistical characteristics of CCI are considered. Our analysis also includes the effects of antenna diversity combining techniques. We employ Gaussian quadrature rules (GQR) to assess the error probability efficiently.

Lifetime maximization of IoT-enabled smart grid applications using error control strategies

The multipath fading and Doppler effect are well-known phenomena affecting channel quality in mobile wireless communication systems. Within this context, the emergence of reconfigurable intelligence surfaces (RISs) brings a chance to achieve this goal. RISs as a potential solution are considered to be proposed in sixth generation (6G). The core idea of RISs is to change the channel characteristic from uncontrollable to controllable. This is reflected by some novel functionalities with wave absorption and abnormal reflection. In this paper, the multipath fading and Doppler effect are characterized by establishing a mathematical model from the perspective of reflectors and RISs in different mobile wireless communication processes. In addition, the solutions that improve the multipath fading and Doppler effect stemming from the movement of mobile transmitter are discussed by utilizing multiple RISs. A large number of experimental results demonstrate that the received signal strength abnormal fluctuations due to Doppler effect can be eliminated effectively by real-time control of RISs. Meanwhile, the multipath fading is also mitigated when all reflectors deployed are coated with RISs.

Use of an adaptive antenna array or a space-time processor at each base station of a wireless network can substantially abate the effects of multipath fading and co-channel interference. Among the expected benefits are higher data rates, greater frequency reuse factors, and overall higher capacity systems as needed to enable wireless multimedia services. Media access control (MAC) protocols which facilitate the deployment of such a processor have been previously proposed and studied. These MAC protocols invoke the delivery of a pilot tone from each packet access unit in the network as needed, so that the array antenna at the associated base station may rapidly adjust its weighting coefficients, or its per branch equalization coefficients, thereby ensuring subsequent reliable communication between the access unit and the base station. This paper considers two modifications to these earlier protocols, both based upon the notion of piggybacking information requests on to the actual information messages and both intended to improve utilization efficiency and mean delay performance. Results show that a maximum link utilization efficiency of 97% is readily achieved with either modification, and that this maximum utilization efficiency is independent of the number of remote users in the network. Note that the utilization efficiency refers to the throughput at maximum loading, i.e., when the remotes always have queued requests. The modifications also help in achieving a considerable reduction in the average delay in low-load regimes: for typical system parameters, the average delay at low load is only about 10% of that produced by the original schemes.

Rician models were used to analyze the desired signals' distributions. The effect of path loss lognormal shadowing and multipath fading was discussed. In this article, we utilized the outage probability to work over the influence to the desired signals which was caused by co-channel interference in microcellular mobile radio systems.

In this paper, a wireless system is considered impacted by Beaulieu-Xie (BX) fading and Rician co-channel interference (CCI). A selection diversity combining technique is used to combat multi-path fading and CCI effects. The expression for the level crossing rate (LCR) is formulated for the receiver with more input branches, and the corresponding curves that have dependence on the signal-to-interference ratio (SIR) are drawn. On the basis of the presented graphs, we quantify the amount of LCR affected by the presence of fading and interference. Additionally, we propose a classification-based predictive model which leverages the previously calculated LCR value as one of inputs among other variables (number of users, base station, the day of the week) with the aim of Quality of Service (QoS) level prediction.

The provision of mobile cloud service calls for a wireless access infrastructure that offers high bandwidth to mobile users. Among all enabling technologies, wireless mesh networks (WMNs) have the advantage of low deployment cost and widely available user equipments. To provide more bandwidth, access points in WMNs are commonly equipped with multiple wireless interfaces (radios) that can operate on multiple non-overlapping channels in parallel. The objective of channel assignments in a multi-channel, multi-radio MWN is to reduce co-channel interference experienced by links so as to increase network capacity while maintaining network connectivity. Prior studies addressing this issue majorly considered effects of co-channel interference at the link layer. In this study, the authors consider co-channel interference at the physical layer. Furthermore, most existing methods are based on heuristic or game theory. This study applies simulated annealing technique to the channel allocation problem. The objective function for this approach is defined as the total signal-to-interference radio (SIR) experienced by each link. To maintain network connectivity, the proposed approach limits the set of assigned channels for each radio. Experimental results show that, compared with traditional heuristic-based and game-theoretic approaches, the proposed simulated annealing algorithm results in more operative links.

This paper analyzes the outage probability of multi-branch dual-hop decode-and-forward (DF) cooperative relaying systems over non-identical Nakagami/Nakagami fading channels. The paper derives an exact closed-form expression for the outage probability with maximum ratio combining considering both the effect of co-channel interference (CCI) and addictive white Gaussian noise. The results of this paper show that a DF cooperative relaying system is more vulnerable to noise than interference for low and moderate SINR, whereas it is more susceptible to interference than noise for high SINR and high diversity order. Moreover, this paper shows that the robustness of the destination against CCI is more important than that of the relay. The results of this paper are verified by Monte Carlo simulations.

Postdetection diversity reception weights and combines all the detector outputs before symbol decision to combat the effects of multipath fading. A theoretical analysis of a postdetection optimal diversity combiner that can minimize the symbol error probability for differential phase shift keying (DPSK) differential detection in the presence of multiplicative Rayleigh fading, and co-channel interference (CCI) is presented. The effect of unequal average powers among diversity branches is taken into account. It is shown that the postdetection maximal-ratio combiner (MRC) described previously by the author is not optimal unless all branches have the same average power. It is also found that the combiner optimized for the effect of CCI (fading induced random FM noise) should weight each branch detector output in inverse proportion to the average CCI power (desired signal power). Assuming two-branch diversity, calculated BER (bit-error-rate) performance of pi /4-shift QDPSK due to AWGN, CCI, and random FM is presented. In addition, the BER due to multipath channel delay spread (which is not treated in the theoretical analysis) is also computed to find the optimal combiner.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The use of smart or adaptive array antennas has attracted considerable interest in the mobile communications community. We investigate the combined use of an adaptive/smart array antenna and Rake receiver (space-time processing) to jointly mitigate the effect of multiple access interference (MAI) and multipath fading in a CDMA system, while taking angle spread into account. We provide simulation results concerning mean bit error rate (BER) performance of such a system for different numbers of antenna elements, numbers of users and angle spreads. The obtained results show that the investigated smart antenna system can effectively combat adverse MAI and fading effects and improve the CDMA system performance.

The fundamental idea of cooperative communications in wireless networks originates from the design of multiple-antenna systems. In multiple-antenna systems, communicating terminals are equipped with multiple antennas to mitigate the effects of multipath fading and optimise the communication rate in the network. Wireless communication nodes like cellular phones and sensor nodes have size restrictions, power supply limitations and are only able to accommodate a limited level of complexity. It is thus unfeasible to equip them with multiple antennas. The effects of multipath fading are critical in cellular, ad hoc and sensor networks because the physical deployment of communicating nodes makes them susceptible to interference. It is imperative to adopt a mechanism to combat fading in such networks. The broadcast nature of the wireless medium makes it easy for the communicating nodes to hear each other. They can share their physical resources specifically their single antennas, thereby creating a virtual multiple-antenna array. Cooperative communications is a concept where several single-antenna nodes cooperate and form a distributed multiple-antenna system which combats multipath fading. In recent years, cooperative communications have received extensive world-wide attention and significant advances in both research and applications have been achieved.

In this research, a classifier is proposed for automatic modulation classification of some common modulation schemes, i.e., BPSK, QPSK, 8-PSK and 16-QAM. Our proposed classifier considers multipath fading effects on the received signal in a non-Gaussian noise environment. Automatic modulation classification is very challenging in real-world scenarios due to fading effects and additive Gaussian mixture noise on modulation schemes. Most of the available modulation classifiers do not consider the fading effects which results in degradation of classification in a blind channel environment. In our work, the channel is supposed to be suffering from excessive additive Gaussian mixture noise and frequency selective fading resulting in low signal SNR. The estimation of the unknown channel along with noise parameters is performed using ECM algorithm and then used in maximum-likelihood classifier for the classification of modulation schemes. Simulation results are presented that show 2 dB improvement in performance than classifier which considers only Gaussian noise in the received signal.

We present frequency hopped spread-spectrum multiple-access (FH-SSMA) employing band-efficient modulations that are phase-continuous during each hop. The particular cases of minimum-shift keying (MSK), and Gaussian minimum-shift keying (GMSK) are studied in detail. Noncoherent sequence estimation on a hop-by-hop basis is considered. Has been evaluated in selective Rayleigh fading with additive white Gaussian noise (AWGN) and the presence of multiple-access cellular interference. Power control is employed for improving the BER performance. This system performance is better than the performance of FH-SSMA with noncoherent binary FSK modulation. >

In recent times, there has been growing interests in integration of voice, data and video traffic in wireless communication networks. With these growing interests, WCDMA has immerged as an attractive access technique. The performance of WCDMA system is deteriorated in presence of multipath fading environment. The paper presents space-time coded minimum mean square error (MMSE) Decision Feedback Equalizer (DFE) for wideband code division multiple access (WCDMA) in a frequency selective channel. The filter coefficients in MMSE DFE are optimized to suppress noise, intersymbol interference (ISI), and multiple access interference (MAI) with reasonable system complexity. For the above structure, we have presented the estimation of BER for a MMSE DFE using computer simulation experiments. The simulation includes the effects of additive white Gaussian noise, multipath fading and multiple access interference (MAI). Furthermore, the performance is compared with standard linear equalizer (LE) and RAKE receiver. Numerical and simulation results show that the MMSE DFE exhibits significant performance improvement over the standard linear equalizer (LE) and RAKE receiver.